1pp Vitamin B12 11

1pp Vitamin B12 11 - Vitamin B12 Spring 2011 2011 Vitamin...

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Vitamin B12 Spring 2011
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Vitamin B12: History • Pernicious (fatal) anemia • Irreversible neurological degeneration f nervous systems of nervous systems
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Vitamin B12: History • Minot , Murphy, Whipple 1920’s iscovered cure for fatal disease – Discovered cure for fatal disease • consumption of large quantities of nearly raw liver cured pernicious anemia Won Nobel Prize 1934
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Vitamin B12: History - Nobel prize also won for elucidating the olecular structure of B orothy molecular structure of B 12 (Dorothy Hodgkins) - Patients could then be treated with synthetic B12
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itamin B12: Structure Vitamin B12: Structure
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Pharmacological Form • Cyanocobalamin most stable pharmacological form sed in vitamin supplements and in foods that – Used in vitamin supplements and in foods that are fortified such as breakfast cereals
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Vitamin B12: Food Sources •S ynthesized solely by microorganisms yy y g – Ruminant animals obtain B12 from microorganisms in gut • Plants do not synthesize B 12 • Only naturally occurring sources of B 12 are foods of animal origin for humans ruits and vegetables • Fruits and vegetables –n o v i t am i n B 12 unless from organisms in dirt • Best source: meat
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Vitamin B12: Food Sources • Dairy products ggs Eggs • Seafood: shellfish very high •B 12 fortified products cereals, meat substitutes, soy milk ,, y
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Vitamin B12: Absorption • Naturally occurring B12 in food ound to protein – Bound to protein – Must be released for absorption astric acid essential • Gastric acid essential • Synthetic B12 in fortified foods – Not bound to protein
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Vitamin B12: Absorption Pepsin cleaves from dietary protein: HCl + Pepsin Dietary Protein-B 12 Protein + B 12 Achlorhydria (reduced production gastric id) acid) impaired absorption common in elderly
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Vitamin B12 Absorption • Two mechanisms of absorption assive Passive – Active
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Vitamin B12: Active Absorption •B 12 in stomach following release from dietary proteins – Binds to R proteins • Found in saliva and gastric juices – Pancreatic enzymes: cleave R protein
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itamin B12: Absorption Vitamin B12: Absorption trinsic factor (IF) Intrinsic factor (IF) • Glycoprotein with a mw of 45,000 Da • Produced in gastric parietal cells in fundus and body of stomach • B12 binds to IF after release from R proteins •I R-B12 complex traverses the entire length of the small intestine • binds to specific receptors located on the brush border of the ileal mucosa
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B 12 •R proteins: salivary glands igher affinity for R proteins than IF in acid pH B 12 R R t h Higher affinity for R proteins than IF in acid pH •Vit B12-R protein + IF moves to duodenum •B12-IF complex resistant pancreatic enzymes B 12 2 R R Stomach B 12 testinal Cell Small intestine Pancreatic B 12 R B 12 Intestinal Cell (ileum) B 12 enzymes Recently discovered: B12 leaves cell unbound, not bound B12 y IF receptor to TCII
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itamin B12: Absorption Vitamin B12: Absorption eceptor has one subunit facing Receptor has one subunit facing outward and one facing into the cell – receptor consists of proteins • cubulin • receptor-associated protein (RAP)
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1pp Vitamin B12 11 - Vitamin B12 Spring 2011 2011 Vitamin...

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